Pretransfusion Testing

Excerpt

Pretransfusion testing is a multistep process that begins with the clinician's order for the right blood product and dose for the patient. It involves the following steps:

1. Positive patient identification

2. Collection of the blood samples of the patient for compatibility testing

3. ABO and Rh blood grouping of the patient and the donor unit

4. Red blood cell Antibody screening on serum/plasma sample of the patient

5. Selection of appropriate blood component

6. Performance of compatibility testing

7. Labeling of the unit with details of the product and the patient identification information

8. Generation of compatibility report that is to be given along with the blood product

It is performed to ensure that the patient is positively identified with any special requirements, that transfusion records and history are reviewed and considered, that antibody detection and identification are performed, and that appropriate units are selected.

Red blood cells have antigenic proteins and carbohydrates on the cell surface. These epitopes are classified into blood groups based on structure and similarities to a parent protein. Patients lacking certain epitopes may develop antibodies when exposed to these antigens through pregnancy, transfusion, or transplantation. Such red cell alloantibodies then lyse transfused red cells that possess the corresponding antigen.

Transfusion and pregnancy are the primary means of sensitization to red cell antigens. In a given population, 2% to 4% of the general population possess irregular red cell alloantibodies. These antibodies can cause hemolytic disease in the newborn or hemolysis of the donor's transfused red cells. If time permits, pre-transfusion testing will identify the antibodies and provide antigen-negative units.

In a "type and screen" procedure, the patient's red cells are typed for ABO and Rh (also known as D), and the patient's plasma is tested for clinically significant red cell antibodies.

A "type and crossmatch" involves selecting, matching, and reserving appropriate red cell components for the transfusion recipient. Many facilities have a Maximum Surgical Blood Ordering Schedule (MSBOS) that indicates when a type and screen are ordered and how many components should be reserved for each type of surgical procedure. Red cell antibodies of clinical significance are produced in response to pregnancy or transfusion; they can cause hemolysis or shortened survival of transfused red cells carrying the corresponding antigen (i.e., acute or delayed hemolytic transfusion reaction).

For this reason, the recipient's plasma is tested for the presence of these unexpected antibodies before red cell transfusion. If a patient has a clinically significant antibody, the transfusion service selects and reserves the appropriate red cell components that do not carry the corresponding antigen. Identifying a patient's red cell antibodies and crossmatching them with the appropriate red cell components can take hours or even days, depending on the antibody or antibodies found. This can be particularly problematic if the intended recipient has autoantibodies. The various pretransfusion testing schemes are summarised in table 1.

Table 1. Pretransfusion testing schemes